Furnace damper control apparatus



March 1953 w. J. MCGOLDRICK FURNACE DAMPER CONTROL APPARATUS Filed Jan. 11,1951

. I Znwentor WILLIAM ,1. MC GOLDRIGK attorney Patented Mar. 31, 1953 FURNACE DAMPER CONTROL APPARATUS William J. McGoldrick, Edina, Minn., Minneapolis-Honeywell Regulator Minneapolis, Minn., a corporation of assignor to Company, Delaware.

Applicationlanuary 11, 1951, Serial No. 205,562

11 Claims.

The. present invention relates to furnace damper control apparatus and more particularly to. apparatus which permits manual operation and. latching of a damper of; a furnace in a firing position and automatic recycling of the damper apparatus to unlatch the damper should the damper be left in a firing position.

In the past it has been found highly desirable to provide damper control apparatus which can be manually controlled at the furnace to place the furnace dampers. in a firing position. Such systems or apparatus usually require extra. timing apparatus and other additional and highly complex control equipments to insure a return of the damper to a normal position under control of. a primary controller. Should the dampers be inadvertently left in the firing. position when such equipment. is not provided, there isdanger of the furnace overheating since the firing position of the dampers usually correspond to one in which. there is. an appreciable amount of draft in they furnace. The present invention utilizes a damper motor of the type disclosed in the copending application of Carl J. Bishofberger on a hydraulic damper motor Serial No. 127,749 filed November 16, 1949, and provides for automatic recycling of the motor after it has been manually latched in the firing, position to insure againstunsafe furnace conditions.

It is therefore an object. of the present invention to provide a. damper control apparatus in which a damper actuator maybe manuall'yoperated to a firing position from the basement without requiring any special or additional controls or motors to perform this function, latched in the firing position and automatically unlatched should the damper actuator be inadvertently left in the latched position.

It is further an object of this invention. to provide in a damper control apparatus a simplified recycling means for insuring that the damper system will not be left in the firing position. These and other objects of this invention will become apparent from a reading of the attached description together with the drawings wherein:

Figure l is a schematic view of the improved furnace damper control apparatus, and

Figure 2 is a plan view of the damper actuator showing the manual latch.

Referring to the drawings for a more detailed understanding of. the present invention, a furnace is, enerally indicated by the reference numeral ID. The furnace is. provided with a stack pipe II, a. draft damper l2, and check damper [3. A pair of stop members M and I5 are provided to limit the opening of the draft and check dampers, respectively. Furnace I0 is further provided with a firing door It for the purpose of introducing fuel into the furnace when it is desired to fire the same. Extending upward from the furnace is a warm air duct I! which is provided with a plurality of branch ducts IE (only one of which is shown in the drawing) leading to the various rooms to be heated by the furnace. Branch duct [8 leads to a space designated as 19 which is desired tobe heated by the furnace. A motor, generally indicated as reference nu meral 20, is used to drive chains 2f, 22 attached tothe draft and check dampers respectively. Chains 2|, 22 are guided by pulleys indicated at 38 and are connected with the dampers to make up a damper control system. These chains are so arranged over the pulleys and are connected to the check and draft dampers respectively that the draft damper is opened while the check damper closes and conversely the check damper is opened while the draft damper closes. Motor 20 is attached to chains 2|, 22 at a pivoted cou-- pling member 23 mounted on the end of an output lever 24 of damper motor 23, lever 24 being attached to the motor proper in a manner later to be described. 1

Motor 20, schematically shown in the Figure 1 and shown in plan view in Figure 2, is an hydraulic type damper actuator similar to that disclosed in the above named copending application of Carl J. Bishofberger. As disclosed in this application of Carl J; Bishofberger, this hydraulic actuator includes a transformer type electric motor indicated schematically at 25, a pump 26, a check valve mechanism 21, and. a piston type operator 28. The transformer motor 25 of this unit rotates the fluid pump 26 to transfer a working medium or fluid from a reservoir 30 through the pump 26 and the check valve 21 to a variable or expansion chamber 29 of the operator 28 wherein the variable chamber 29 is expanded against a piston member 3| attached to one end of the output lever 24. Output lever 24 is pivoted on a link 32 pivotally mounted on a casing 33 enclosing the hydraulic actuator. Piston member 3| moves downwardly within the casing 33 under the force of expansion of the variable chamber 29 of operator 28, and the end of output lever 24 attached to the chains 2|, 22 moves upwardly from the position shown in Figure 1 to close the check damper I3 and open the draft damper l2. Piston 3! is urged upwardly within the casing 33 against the variable chamber 29 by means of a spring 34 housed within the casing 33 to form a spring return unit. With actuator in a deenergized position, check valve member 2'! is in a normal position and a by-pass is provided through this unit from the operator 28 to the reservoir 36 such that the fluid in the variable chamber is urged back to the reservoir by means of the operation of spring 34. No positive connection exists between the variable chamber 29 of operator 28 and piston 3i and consequently the piston member may be urged downwardly merely by the expanding force of the variable chamber 29 or by manual manipulation of the output lever 24 against the spring tension of spring member 34. For reasons to be later noted, a latch member 3'5 (shown in Figure 2) is mounted on the piston end of output lever 24, the latched member being adapted to be pivoted into the position where it is disposed between the casing 33 and the output lever 24 to hold the lever in the raised position against the tension of spring 34. The latch is so constructed and mounted to the lever 24 and piston 3! that it is pivoted oil center and is normally disposed in an unlatched position. When the latch is raised to a latched position the tension of spring 34 is required to retain it there. The latch 35 is disengaged merely by urging the piston 31 downwardly to remove the force of the spring acting against the latch at which time the latch pivots free to a disengaged position as it is shown in Figure 2.

Transformer motor 25 of actuator 26 which is shown and described in detail in the above mentioned Bishoiberger application, is disclosed herein in some detail merely for a better understanding of the manner in which it is to be con trolled. Motor 25 is of a four pole type having an 0 shaped yoke 44 with four pole piece members 39 thereon and with a pair of primary windings 3E and a pair of secondary windings 31 mounted thereon. The primary windings are mounted on diametrically opposite portions of two legs of the yoke of the motor and the secondary windings are mounted in a diametrically opposite relationship upon opposite portions of the same two legs of the yoke. The pole pieces 39 of the motor have shading coils 43 mounted thereon in the same position such that the motor will be of a unidirectional type as will be later noted. Primary windings 36 of the motor 25 are I energized continuously and directly from the source of power 4! through a switch 42 by means of conductors 43. These windings may be connected in series or in parallel with the source of power. When energized, these windings set up the flux in the yoke 44 of the motor 45 which circulates within the yoke until the secondary windings 31 are short circuited. The secondary windings 3'! are adapted to receive their energization from the primary flux of the primary windings 36 and are connected in series with one another and a primary controller 50 to be later described. When the secondary windings 31 are short circuited, an energizing current created by the primary flux flows in the secondary windings to generate a counter flux thereby saturating portions of the yoke 44 and directing the primary flux to flow through the pole pieces 39 of the motor. Shading coils on the pole pieces 39 set up a rotating flux field which cooperates with a rotor (usually of the squirrel cage type) to cause rotation of the rotor in the direction determined by the rotating flux field. The rotor 45 is connected by means of a shaft (not shown) to the pump 26 which is indicated schematically in the drawings. This pump when operating takes fluid from the reservoir or sump 30 and transmits it to the check valve 21 under pressure. When pressure is applied to the check valve from the pump side, the check valve opens a passage communicating with the operator 28 and closes a by-pass communicating from the operator 28 to the sump. Fluid from the reservoir thus flows from the pump 26 through the check valve 21 to the operator 28 to expand the variable chamber 25 of the operator 28. Movement of the variable chamber 29 of the operator 28 against the piston 3! causes the output lever 28 to move in the manner described above. When energized, the motor would generally operate the output lever to the limit positions of the dampers at which point the transformer motor will stall under the build up of pressure in the pump. Due to a certain amount of leakage past the pump 26, pressure of the medium against the check valve 21 drops and motor 25 will operate intermittently and periodically to maintain pressure of the system as long as the primary controller 56 continues to call for operation of the actuator 20. When the primary controller is satisfied, the motor is deenergized and rotation of the pump 26 stops. At this point leakage past the pump 25 and check valve 21 permits the check valve to open the by-pass to the reservoir 3!! and the fluid medium is trans mitted from the operator 28 back to the reser voir 38. The piston 3i urged by spring 34 supplies the force against the Variable chamber of operator 28 to urge the medium back into the reservoir 30. I

As noted above there is no positive connection between the variable chamber of operator 28 and piston 3!. Consequently output lever 24 may be manually moved to vary the position of the dampers of the system merely by overcoming the tension of the spring 34 without effecting the remaining components of the actuator 20. When it is desired to fire the furnace, output lever 24, may be raised to open close check damper I3 and the latch 35 inserted to hold the output arm and consequently the dampers in firing position. Upon completion of the firing operation, the latch is returned to its normal position, and the output lever 24 and hence the dampers return to their normal positions by means of the spring 34. The apparatus is then under the control of the primary controller 50.

As noted above, motor 25 is controlled by means of a short circuit connection to its secondary windings 31 by means of the primary controller 50. Primary controller 50 is a room thermostat which is located in the space i9 heated by the furnace Hi. This thermostat may be of any conventional construction and is shown as comprising a bimetallic element 5| to which is secured a contact arm 52 adapted to engage a fixed contact 53. Cooperating with the contact arm 52 is a magnet 54. This magnet is adapted to exert a tendency to hold the arm 52 in engagement with contact 53 when so moved. In this manner it is necessary for a temperaturepchange to occur after the contact arm 52 has moved into engagement with the contact 53 in order for this arm to separate from the contact 53. By reason of the magnet 54, it is thus necessary for there to be a temperature differential between opening and closing of the thermostatic switch. and accordingly any tendency toward the chat tering operation thereof is avoided. This therthe draft damper l2 and mostatic switch is known as the primary controller of the damper actuator 29 for reasons which will be obvious in the description below.

Furnace l is further controlled by means of a limit control generally designated by the reference numeral 50. This limit control consist of a bimetallic element til positioned in a portion 59 of furnace it! generally known as the bonnet which bimetallic element is designed to operate a plurality of switches associated therewith. In order that the switches and the general construction of the limit control can be more clearly illustrated, the end face of this unit, in Figure 1, is shown enlarged and revolved through an angle of 90 degrees. Secured to the bimetallic element BI is a rod 62 which is rotated thereby as the temperature of the bonnet 59 of the furnace is changed. Secured to the inner end of the rod 62 is a pair of cams 63, 64. The cams 63, 64 are slida'bly positioned adjacent one another on shaftSZ and are movable relative to one another being secured to the shaft by means of an adjusting nut 65. Cam 63 having a single rise and dwell'portion thereon cooperates with a cam follower 56 mounted on a pivoted switch holder 61. Switch holder 87 and consequently the follower or finger 66 are spring biased by means not shown to a position where the follower engages cam 63 at all times. Holder 67 mounts a mercury switch 68 of any conventional type, this switch being in a closed position when the cam follower is on the dwell portion of cam 63, as can be seen in Figure 1. As shaft 62 rotates (counterclockwise as seen in the enlarged view of the limit control) and hence switch holder 61 and switch 68 in a clockwise direction opening the circuit through the switch contacts. The inner cam 64, as seen in Figure 1, has a single rise portion 80 which in effect is an arm pair of switch contact blades 8|, 82 to urge the contacts thereon into an engaged position as shaft 62 is rotated. Blades BI, 82 are .made of a flexible electrically conductive material, the blade Bl being somewhat longer than th blade 82 and being adapted to be engaged by the arm 80 of cam 64. In the normal position, the contacts on the blades BI, 82 are in open or separated position and as the shaft 62 is rotated, the arm 80 engages blade 8| and urges it into engagement with blade 82 to make a circuit therethrough. As the temperature of the furnace increases rod 62 will continue to rotate and arm 80 will be urged past the blade M at which point the contacts or electrical circuit therethro-ugh will open. As the temperature of the furnace decreases and the rod 62 rotates in a clockwise direction as seen in the enlarged figure, engagement of arm 80 with contact 8| does not operate to close the circuit between contacts 8!, 82. It will be noted in contrast to switch 68, the switch formed by the contacts BI, 82 will not be made for any substantial period of rotation of shaft 62 as the temperature of the furnace increases. While it has been noted abov that thermostat 50 is the primary controller for controlling the operation of the actuator 20 in adjusting the dampers of furnace Ill, it should be noted that the limit control 60 through its mercury switch 68 in response to abnormal furnace temperature conditions operates also to control the operation of damper motor 20 as a safety device. This operation will become evident as the disclosure proceeds. The contacts 8!, 82 which are also operated by the bimetallic element 6| of limit concam 63 urges follower 56 adapted to contact one of the 6 trol 80 are known as the recycling contacts which further control the operationof damper motor or actuator independent of the thermostat or, primary controller '50 and mercury switch 68 for the purpose and in the manner to be later described.

Operation The elements of damper control system and the furnace are shown in Figure l in the position which they occupy when the temperature of space it is satisfied or at a predetermined level and when the latch is in an unlatched position, the bonnet temperature of furnace 10 being normal. Should the temperature of space l9 drop sufficiently to operate the thermostat or primary controller 55, contacts '52, '53 of this thermostatic element will close. The primary windings 35 of the motor 25 are normally continuously energized as indicated above, and closure of the thermostat contacts will complete a shorting circuit with the secondary windings i i of the motor 25 as follows: from one end terminal of secondary wind ings 37 of motor 25 in series to a terminal board Hi, conductor H to the normally closed contacts of mercury switch '68, conductor 72, bimetallic element 5! of thermostat 59], movable contact 52 to stationary contact 53, conductor 13, and conductor 74 through terminal board 10 back to the other end terminal of secondary windings .31 of motor 25. It will be noted in the above circuit that the limit control 6.9 in its normal position, that is with the bonnet temperature of the furnace it within a safe range, is normally closed. The short circuit for secondary windings iii of motor 25 will cause -the rotor 40 of motor 25 to rotate thereby operating pump .25 and transferring the working medium from the reservoir 36 through the check valve 21 to the operator 28 of the actuator. As the variable chamber 29 of operator 28 expands, piston 3| moves downwardly urging the end of output arm 24 up to close the check damper Q3 of furnace H] and open draft damper l2. This increases the draft of the furnace thereby increasing its temperature and consequently increasing the temperature of the space l9. Generally the actuator 20 will operate to a limit position defined by the stop M on the draft damper. At this point a build up in pressure in the pump will aifect a stalling Or stoppage of the rotation of rotor 48 of motor 25 and thereafter the motor will remain in a stalled position periodically turning over to maintain pressure in the operator 28 as long as thermostat 59 remains un satisfied. When space [-9 is sufliciently warm to satisfy thermostat 50, its contacts will open,

thereby opening the shorting circuit for secondary windings 3! and the rotor 49 will no longer continue to rotate. The leakage past the pump 26 noted above permits the check valve to open the bypass to the reservoir and the working medium in the variable chamber 29 of operator 28 will be forced by means of the tension of spring 34 on piston 3! back into the reservoir 30. As the piston is urged upwardly the damper arm 34 is urged down thereby closing the draft damper and opening the check damper.

With the draft damper i 2 in the open position, the check damper 13 in the closed position and room thermostat 50 still unsatisfied, it is pos sible for the temperature of the bonnet 59 of the furnace Hi to reach an unsafe condition wherein the shaft 82 will have rotated the cams 63, 64 to operate the switch 68 and the recycling contacts 8|, 82. Normally furnace It would furnlsh enough heat to th space l9 to satisfy the predetermined temperature requirement of the space before the furnace would reach such an overheated condition. If, however, such an overheated condition is approached, the recycling contacts would first close to establish a shunt circuit to be described below around the thermostat and the limit switch 68 shorting out the secondary windings 37 of motor 25. Since the thermostat 50 is already in a closed position no change will take place in the operation of the damper motor 20. Upon continued rise in temperature of the furnace, however, switch 68 will be operated by means of cam 63 engaging the finger 68 of switch holder 61 to open this normally closed limit switch. Since switch 68 is located in the primary controlling circuit described above in series with thermostat 59, the opening of this switch will break or open the circuit described above. This will stop rotation of motor 25 and hence operation of the pump A 26 and the actuator will resume the normally deenergized position wherein the check damper is opened and the draft damper is closed in the manner described above.

When it is desired to fire the furnace, it is generally desirable to have the draft damper open and check damper closed for proper firing operation. Should the damper control system be already in such a position, that is the thermostat closed and the motor 20 operated to a point where the draft damper is already open, firing of the furnace can take place without further control. If, however, the draft damper is closed and the check damper is open, it is desirable to open the draft damper and close the check damper before commencing firing operation. This can be done by manually moving output lever 24 of actuator upward to open the draft damper l2 and close check damper l3 and flipping latch in place to hold the piston 3! in an intermediate lowered position against tension of spring 34. The furnace can then be fired without the requirement of further operation of the actuator or any of the control devices. When firing is completed the control of the actuator is returned to the thermostat by simply urging arm 24 slightly upwardly and releasing latch 35 allowing the damper arm to fall into its normal position. If, however, after completion of the firing operation the damper arm 24 is left in a latched position, there is danger that this draft open position of the furnace is apt to cause serious overheating of the furnace unless control of the actuator 20 is returned to the primary controller 513. It is for this reason that the cycling contacts 81, 82 are provided in the limit control 60. As furnace temperature increases with the dampers located in the firing position of the furnace, the bimetallic element iii of limit control will respond to the increase in temperature and rotate shaft 52 and consequently cam 64 into engagement with the recycling contacts to operate thesame. As the raised portion 80 of cam 64 engages flexible blade 8! of the recycling contacts, it urges blade SI and its contact thereon into engagement with blade 82 setting up an auxiliary circuit for the operation of actuator 20 which is as follows: from one end terminal of secondary windings 31 of motor 25, terminal board 70, conductor I4, conductor 16, to switch contact blades 8i and 82 of the recycling switch, conductor H to conductor I I, and terminal board H! back to the other end terminal of secondary windings 3! of motor 25. It will be noted that the above circuit shorts cal the-windings 31 of motor 25 independent of the primary controlling circuit of the thermostat 50 and limit control 60. The shorting circuit thus set up causes rotation of rotor 40 of motor 25 and operation of pump 26 to expand the variable chamber 29 of operator 28. Since the piston is no longer in engagement with the end of the variable chamber, no efiect will be had on the output arm which up to this point has been latched in firing position. However, when the chamber expands to the point where it engages the piston 3|, it will urge the piston downwardly beyond the latched position of arm 24 thereby dropping out the latch 35 and placing the output lever 24 again under control of the actuator 20. The damper control system will remain in a damper open position as long as the recycling contacts remain closed and this will generally cause continued rise in temperature of the bonnet 59 of the furnace and hence further rotation of Shaft 62. Continued rotation of shaft 62, however, will cause the finger of cam 84 to slide under the contact arm 8| opening the recycling contacts and allowing the actuator 20 to return to its normally deenergized or damper closed position in the manner described above. Thus it will be seen that the limit control serves two functions, namely that of shutting down the furnace as a safety device when the furnace becomes overheated and also operating a pair of recycling contacts to recycle the actuator 20 if it should be left in a latched position.

While my improved furnace damper apparatus has been described as using the particular type of motor and a particular type of recycling contacts, it should be understood that any type of damper motor capable of manual manipulation and latching and any type of control device or switch contacts capable of responding to increased furnace temperature condition may be utilized herein. Therefore in considering this invention it should be kept in mind that the present disclosure is intended to be illustrative and the scope of the invention should be determined only by the appended claims.

I claim as my invention:

1. Inoombination, motor means adapted to operate a damper of a furnace between two positions, a main control means including a device responsive to a condition indicative of the demand for operation of said furnace for controlling said motor means, limit control means including a device responsive to a desired limiting condition of the furnace and operative to control said motor means independently of said main control means, manually operated means included on said motor means for latching said damper intermediate said two positions, and means included in said limit control means operating as said limiting condition of the furnace is approached to control said motor means independently of the operation of .said main control means.

2. In combination, motor means including an operating lever adapted to be connected to a damper control system of a furnace and operate a damper between two positions, thermostatic control means adapted to respond to the temperature of a space to be heated by the furnace for controlling the operation of said motor means, limit control means including a device responsive to a desired limiting condition of the furnace and operative to control said motor means independently of said thermostat, latching means positioned on said operating lever of said motor means and providing for manual latching of said lever in one position of said damper, and switch means included in said limit control means momentarily operative upon said limiting condition being approached to control the operation of said motor means independently of said thermostat and said limit device to disen age said latch means.

3. 'In combination, motor means including an output lever means adapted to be connected to a damper control system of a furnace and operate a damper on the furnace between two positions, manual means on said lever for latching said lever in one of said two positions, a thermostat means responsive to a condition indicative of the need for operation of the furnace for controlling said motor means, limitcontrol means adapted to respond to a condition of said furnace for controlling said motor means concurrently with said thermostat means, and auxiliary control means operated by said limit control means as it approaches said furnace condition to operate said motor means independently of said thermostat means to release said manual means on said output lever should it be left in the latched position.

4. In combination, spring return motor means including an output lever adapted to be connected to a damper control system of a furnace and operate a damper on the furnace between two positions, said output lever being .adapted to be moved to one of said two positions manually, manual means on said output lever for latching said lever in said one of said two positions, thermostatic means responsive to a condition indicative of the need for operation of the furnace for controlling an energization circuit for said motor means, limit control means adapted to respond to a condition of the furnace for controlling said motor means, said thermostatic means and limit control means being connected in said energization circuit for said motor means, and auxiliary control means operated by said limit control means as it approaches said furnace condition to operate said motor means independently of said thermostatic means and adapted to release said manual means on said output lever when it has been left in a latched position.

5. In combination, spring return motor means including an output lever adapted to be connected to a damper control system of a furnace and operate a damper on the furnace between two positions, said output lever being adapted to be moved to one of said two positions manually, manual means on said output lever for latching said lever in said one of said two positions, thermostatic means responsive to a condition indicative of the need for operation of the furnace for controlling an energization circuit for said motor means, limit control means adapted to respond to a condition of the furnace for controlling said motor means, said thermostatic means and limit control means being connected in said energization circuit for said motor means, and auxiliary control means operated by said limit control means as it approaches said furnace condition to operate said motor independently of said manual means and adapted to release said manual means on said output lever when it has been left in a latched position, said auxiliary control means being connected in a circuit in parallel with said energization circuit for said motor.

6. In combination, spring return motor means operative to one position by means of electrical energy and returnable to a second position by means of a spring, said motor when deenergized being adapted to be manually moved to said first position, means for manually latching said motor means in said first position, thermostat means having control means thereon for controlling electrical energy to said motor means to cause it to move to said one position, limit control means including a controller in series with said thermostat means for controlling electrical energy to said motor means, said 1imit control means responding to .a condition indicative for the need for returning said motor means to said second position, and recycling control means operable over a limited range of response of said limit control means for controlling electrical energy to said motor independently of said thermostat such that said motor means may be operated to disengage said manual latch.

7. In combination, motor means including an output lever means adapted to be connected to a damper contro1 system of a furnace and operate a damper on the furnace between two positions, said motor-means being of the spring return type being operated to one of said two positions by means of electrical energy and returnable to a second position by means of a spring, means included in said motor means for permitting said output lever to be manually moved to said one position and latched therein, thermostatic means including electrical control means thereon :for controlling electrical energy to said motor means, limit control means adapted tobemounted on the furnace and respond to a condition of said furnace, said limit control means including a controller connected in series with said thermostat for controlling electrical energy to said motor means, and recycling means operated by said limit control means over a limited range of said condition of the furnace for controlling electrical energy to said motor independently of said thermostat and said limit control means, said recycling control means providing operation of said motor means to remove said manual latch when said output arm has been left in a latched position.

8. In combination, motor means adapted to operate a damper of a furnace between two positions, primary control means responsive to the need for operation of the furnace to establish a circuit for the energization of said motor means, limit control means responsive to a condition indicative of the need for shutting down the furnace for opening said energization circuit of said motor means, and recycling control means operative in response to operation of said limit control means for temporarily establishing an auxiliary energization circuit for said motor means independently of said first named energization circuit.

9. In combination, motor means including an output lever means adapted to be connected to a damper control system of a furnace and operate a damper on the furnace between two positions, means included in said motor means per mitting a manual operation of said output lever means to one of said two positions and latching of said arm in said one of said two positions, a primary control means responsive to the need for operation of the furnace for establishing a circuit for the energization of said motor means to operate said motor means to said one of said two positions, limit control means responsive to a condition indicative of the need for shutting down the furnace for opening said energization circuit for said motor means and permitting said damper arm to move to a second of said two positions, and recycling control means operati ve in response to operation of said liniltcontrol. means for temporarily establishing an auxiliary energization circuit for said'motor means independent of said first named energization circuit, said recycling control means permitting limited operation of said motor means to said one of said positions and thereby releasing said manual latch should said damper arm be left in a latched position.

10. In combination, motor means for operating a damper of a furnace between a fire increasing and a fire decreasing position under control of a main controlled switch, a damper actuator positioned by said motor means and adapted to be connected to a damper of the furnace to position the same, means for manually moving said ac-.

tuator and said damper independently of said motor means into a fire increasing position for firing purposes, a limit control adapted to. respond to a desired limiting condition of the furnace for causing said actuator to move said damper into said fire decreasing position, circuit connections for energizing said motor means independently of said main switch for operating said motor means when said actuator has been manually moved to a fire increasing position, and means for causing said limit control, to render said circuit connections effective as said limiting condition is approached.

1 11. In combination, motor means for operating a damper ofa furnace between a fire increasing and a fire ,decreasingposition under control or a main controlling switch, la damper actuator positioned by-said motor meansfand adapted to be connectedto'a' damper of the furnace to position the same, means forlmanually moving said actuator and said damper independently of said motor means into a fire increasing position and holding said actuator in said fire increasing position for firing purposes, a limit control adapted torespond to a desired limiting condition of the furnace for causing said actuator to move said damper into said fire decreasing position, circuit connections for energizing said motor means independently of said main switch for operating said motor means when .said actuator has been manually moved to a fire increasing position to release said actuator from said fire increasing position, and means for causing said limit control to render said circuit connections efiective as said limiting condition is approached.

I WILLIAM J. McGOLDRICK.

REFERENCES CITED The following references are of record in the 

